Amiga and Atari fans used to lord over their Apple-eating brethren the fact that Cupertino never moved to the most advanced 68k processors — so for a while, thanks to 68060 accelerator cards, the fastest thing running Macintosh software was an Amiga (or Atari). After all these years, the Macintosh community is finally getting the last laugh, as [zigzagjoe] demonstrates an actual Macintosh booting with a 68060 CPU for the first time in a thread on 68KMLA. Video or it didn’t happen? Check it out below.
The Mac in question is a Quadra 650, which is a good choice since it was about the last thing Apple sold before switching to PowerPC, and ran the 68040 processor. [Reinauer] had already produced a 68040-to-68060 socket adapter (the two chips not being pinout compatible), so the hardware part of the battle was already set. Software, however? That was a different story, and where [zigzagjoe] put in the effort.
We’re spoiled by decades of backwards compatibility in the x86 instruction set; Motorola wasn’t as kind back in the day, and the 68060 isn’t fully compatible with the earlier 68040’s instruction set. They did provide a translation that [zigzagjoe] was able to build into his custom ROM, though, which is how he’s able to get the Mac to boot and install System 7.1, the newest version that would boot.
Alas, the full 66 MHz clock speed [zigzagjoe] proved unstable. To make branch prediction work, he had to clock down to 50 MHz. Considering the ‘040 clocked at 25 MHz in the Quadra 650, that’s still a considerable improvement in clock speed.
At 66 MHz and giving up branch prediction, DOOM runs at 16.4 FPS. It slowed down (14.3 FPS) at 50 MHz, and branch prediction. We expected branching to have a greater impact, but apparently not. While DOOM is perhaps not the best benchmark on this hardware, it does answer the most important question you can ask of any bit of kit: yes, it does run DOOM!
While Apple has long since abandoned the 68k in favour of PPC, x86, and finally their own implementation of ARM, there are always enterprising upgraders.
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This articles is written by : Nermeen Nabil Khear Abdelmalak
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